The present invention is directed to electrical inductive circuit elements, such as inductors and transformers, and especially to small electrical inductive circuit elements having a low profile that may be reliably and economically manufactured in production quantities.
Prior art inductive elements that require a magnetic core structure commonly provide a cutout aperture through a dielectric substrate for insertion of a ferromagnetic or other magnetic core structure. The core structure may already bear the required windings for effecting inductive coupling, or the required windings may be incorporated into circuit traces arrayed upon the substrate. There are problems with using such a structure, especially in applications where small inductive circuitry having a low profile is desired. Chief among the problems with such an approach are the room required to accommodate an inductive element and its supporting electrical circuitry. In addition, the large size of prior art inductive circuitry necessitates situating associated circuit elements a distance removed from the inductive element. Such physical separation among circuit elements introduces capacitance and inductance into the circuit as well as increased trace lengths, all of which may contribute to increased losses. Such an introduction of capacitive and inductive factors into circuitry is a problem in power supply output circuits as well as in any LC (inductance-capacitance) filter application; the increased capacitances and inductances reduce transient response of such circuits and increase losses.
An attempt to ameliorate the problems associated with assembling inductive circuit elements is described in U.S. Pat. No. 5,781,091 issued Jul. 14, 1998 to Krone, et al. for xe2x80x9cElectronic Inductive Device and Method for Manufacturingxe2x80x9d. Krone, et al. describe an assembly structure and process for manufacturing that structure that provides an inner board layer with an aperture. The apertured inner board layer is situated atop a laminate that includes an insulating layer and a copper foil layer. The insulating layer faces the inner board. The aperture is partially filled with a thin layer of fiber filled epoxy and a ferromagnetic core is installed within the aperture atop the fiber filled epoxy layer. Another layer of fiber filled epoxy is added on top of and within the center of the core completely covering the core and embedding the core in the fiber filled epoxy, an insulating material. A second laminate similar to the first laminate is then applied atop the inner board to complete a board stack, with the insulating layer of the second laminate facing the inner board.
Plated through-hole structures are provided traversing the board stack; circuit traces are created on outer faces of the board stack by etching the copper foil layers. The circuit traces are connected with the through-hole structures to establish electrical paths that encircle the core thereby establishing an inductive coupling circuit with the core.
One shortcoming of the Krone, et al. structure relates to the employment of fill material within the aperture that covers the core. The magnetic core is placed within an aperture that is filled with a material that is at least somewhat viscous at temperatures encountered during processing steps contemplated by Krone et al. As a consequence, the core is liable to xe2x80x9cfloatxe2x80x9d within the aperture during processing. The varied positioning that a core may assume during processing because of such an ability to float means that the through-hole structures required by Krone et al. for forming loops about the core for inductive coupling may not be placed with respect to the core to avoid intercepting the core. That is, the cores can float sufficiently that one may intercept the core while drilling or otherwise forming the through-holes. This placement precision limitation presents less of a problem for inductive devices that are sufficiently large. However, for inductors that are small enough to be useful in today""s circuits for such applications as board mounted power supply products or the like, the size of the core is sufficiently small that manufacturing yields for such products will be too low to make the use of the Krone et al. structure an economically worthwhile approach. Further, the tolerances that are required for producing the Krone et al. structure are likely to be too large to permit fabrication of products small enough for use as board mounted power supply products.
There is a need for an improved structure for electrical inductive element and method for manufacture of the element that provides precision manufacturing of small power products with tightly controllable tolerances.
An apparatus for establishing inductive coupling in an electrical circuit arranged on a plurality of dielectric substrates, the plurality of dielectric substrates being in a substantially abutting relationship and presenting a plurality of substantially parallel planar expanses, includes: (a) at least one first core segment situated in at least one first depression provided in a first planar expanse of the plurality of planar expanses; (b) at least one second core segment situated in at least one second depression provided in a second planar expanse of the plurality of planar expanses; (c) a selected second core segment arranged for establishing magnetic flux coupling with a selected first core segment to establish a selected magnetic core structure; (d) a plurality of electrically conductive through-hole structures traversing at least one substrate of the plurality of substrates; (e) a plurality of electrically conductive circuit traces arrayed upon at least two planar expanses of the plurality of planar expanses. The plurality of conductive traces and the plurality of through-hole structures cooperate to effect establishing inductive coupling.
The method for manufacturing the apparatus produces an electrical circuit arranged on at least one dielectric substrate. The electrical circuit establishes inductive coupling with a magnetic core structure. The at least one substrate presents a plurality of substantially parallel planar expanses. The method includes the steps of: (a) providing at least one substrate; (b) creating a first depression in a first planar expanse of the plurality of planar expanses; (c) creating a second depression in a second planar expanse of the plurality of planar expanses; a portion of the second depression being substantially in register with a portion of the first depression; (d) situating a first core segment in the first depression; (e) situating a second core segment in the second depression; the first core segment effects magnetic flux coupling with the second core segment to establish a magnetic core structure; (f) providing a plurality of electrically conductive circuit traces arrayed on at least two of the planar expanses; (g) providing a plurality of electrically conductive through-hole structures traversing at least one substrate; (h) coupling the plurality of conductive traces and the plurality of through-hole structures to effect establishing inductive coupling.
It is, therefore, an object of the present invention to provide an apparatus for establishing inductive coupling in an electrical circuit, and a method for manufacture therefor, that facilitates precision manufacturing of small power products with tightly controllable tolerances.
Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention.